Patent GB-938479-A (GB)
Title: Cellulosic insulation material and electrical apparatus embodying such material
IPC: H01B3/48
Filed: 1960-08-15
Abstract: Enamels comprising (1) a mixture of a glycidyl polyether resin and a urea-aldehyde or melamine-aldehyde resin, with or without a phenol-aldehyde or polyvinyl formal resin, or (2) a mixture of a heat-hardenable organosiloxane and a polyamide containing residues from unsaturated dicarboxylic acids, or (3) a mixture of a polyvinyl formal and a phenolaldehyde resin (see Group IV(a)) are used to coat wires and transformer coils, in a coating tower, by means of coating dies, or by flowing or dipping.  The enamel is baked after application.  It may be applied to bare copper wire or to wire covered with cotton, asbestos, glass-fibre or other fibrous or cellulosic materials.  These fibrous materials may be applied before, at the same time as or after the enamel.ALSO:Wire enamels comprise (1) a mixture of a glycidyl polyether resin and a urea-aldehyde or melamine-aldehyde resin, with or without a phenol-aldehyde or polyvinyl formal resin, or (2) a mixture of a heat-hardenable organosiloxane and a polyamide of special kind, or (3) a mixture of a polyvinyl formal and a phenolaldehyde resin.  The glycidyl polyether resin is made by reacting a polyhydric phenol and an epihalohydrin in an alkaline medium.  Suitable phenols are 4,41-dihydroxy-diphenyl-dimethyl-methane, 4,41-dihydroxy-diphenyl-methane, and 4,41-dihydroxy-diphenyl-sulphone.  The product may be dissolved in methyl-"Cellosolve" (Registered Trade Mark) and xylene and a solution of butylated urea-formaldehyde in xylene added to form the enamel. The polyamides referred to include in the polymer molecule residues of three kinds, those of: (1) polymethylene diamine, (2) unsaturated dicarboxylic acid, and (3) isophthalic acid, terephthalic acid or an aliphatic dicarboxylic acid having no ethylenic unsaturation and from two to eight non-carboxyl carbon atoms, or of the first two kinds only.  They are made by mixing and heating the unsaturated dicarboxylic acid or its anhydride or ester and the diamine or a polyamide reaction product which has terminal amino groups and is derived by reacting a diamine and the acid of group (3) above in a non-reactive solvent.  Suitable unsaturated acids are maleic, fumaric and citraconic.  Suitable diamines are ethylene diamine, 1,3-propylene diamine, 1,4-butylene diamine and hexamethylene diamine.  The resulting polyamides are mixed and reacted with organosiloxanes in solvents such as butanol, xylene, or dichlorobenzene to provide enamels.ALSO:Cellulosic insulation material contains 0,02 to 10% by weight of a mixture of stabilizing agents to reduce loss of physical strength at elevated temperatures with passage of time.  The mixture contains dicyandiamide (up to 85%), and at least one of: melamine, triethylmelamine, triphenylmelamine, diallylmelamine, polyacrylamide, succinonitrile and diphenylguanidine.  The cellulosic material may be paper, cotton cloth, cotton tape, pressboard or wood.  The material may also contain a synthetic resin of the type having a water-soluble condensation intermediate, e.g. a urea-formaldehyde resin, a melamine-formaldehyde resin, an epoxy resin or a phenol-formaldehyde resin.  The stabilizers may be incorporated in paper in the course of manufacture by forming and partially drying the paper, passing it through a solution of the stabilizers, and then completing the drying, or by adding the stabilizers to the furnish.  Alternatively, it may be sifted or otherwise applied to the paper as the latter is wrapped about conductors or coils in electrical apparatus.